Warranties are not as comprehensive with the RV industry as they are in automotive. Many dealers only service units they sold, even though technically they can work on others. Brands have varying levels of coverage, and varying degrees of desire to cover their products.
A few do seem to have more favorable customer opinions than others. Grand Design owners seem most happy and in varying degrees Winnebago, K-Z, Jayco, and then it falls to the others,
Warranty coverage as far as duration can be seen as something of an indicator by some, and in general Jayco, K-Z, some Keystones, Palomino, a few others offer warranty periods longer than one year.
Remember, the warranty from the manufacturer is for what they build, appliances, frames, axles, etc are warranted separately by the companies that provided them.
Your best chance at a unit with few problems is to do a very thorough walk through BEFORE delivery, and have everything addressed prior to taking possession, when you are in the position of power.
Hope this helps.